1. Field of the Invention
This invention relates to an image recording apparatus arranged to be capable of recording not only moving images but also still images.
2. Description of the Related Art
In the field of magnetic recording, a demand for high density recording has increased of late. To meet this demand, video tape recorders (hereinafter referred to as VTRs) have come to be arranged to perform magnetic recording at a higher density by lowering the traveling speed of a magnetic tape employed as a recording medium.
The lower traveling speed of the tape, however, brings about the following problem: If an audio signal is recorded with a fixed head, for example, it is impossible to make the relative speeds of the tape and the fixed head sufficiently high. The quality of reproduced sounds degrades under such a condition. In one of methods for solving this problem, the length of recording tracks to be handled with a rotary head on the tape is extended to be longer than the conventional length and an audio signal which has been time-base compressed is recorded within the extension areas of the tracks one after another.
More specifically, this method is carried out as follows: It has been practiced to wrap the magnetic tape at least 180 degrees around a rotary cylinder which carries rotary heads in a rotary 2-head helical scanning type VTR. Whereas, in accordance with this method, the tape is wrapped at least (180+.theta.) degrees around the rotary cylinder; and an audio signal which has been pulse-code modulated (PCM) and time-base compressed is recorded within the additional wrapping part .theta..
FIG. 1 shows the tape transport system of the VTR of the above-stated kind. FIG. 2 shows recording tracks formed on a magnetic tape by the VTR of FIG. 1. In these figures, a reference numeral 1 denotes the magnetic tape. A numeral 2 denotes a rotary cylinder. Numerals 3 and 4 denote heads mounted on the rotary cylinder 2. A numeral 5 denotes video signal recording areas of the recording tracks formed on the tape 1. A numeral 6 denotes a PCM audio signal recording area of the recording track. The video signal recording area 5 is arranged to be traced by the heads 3 and 4 within the angle range of 180 degrees around the rotary cylinder 2 and the PCM audio signal recording area to be traced within the angle range of .theta. around the rotary cylinder 2.
A method for recording a still image within the PCM audio signal recording area 6 in the form of a digital signal has been proposed as an application example of the method of recording a digital signal in another area while a video signal is recorded within one area as mentioned above. Information about a still image can be completely recorded on the magnetic tape by scanning a plurality of the above-stated PCM signal recording areas 6, if a single still image is to be recorded. This method not only permits still image shooting by using the same recording medium as the recording medium used by the conventional apparatus for shooting a moving image but also makes it possible to obtain a still image of a higher picture quality than such a still image that is obtainable by reproducing a video signal from one and the same track by stopping the tape travel in the conventional VTR.
However, the prior art example described above has had the following drawbacks because it has been arranged to perform still image shooting by using a lens system and a lens control system which are intrinsically designed for shooting moving images:
(1) In shooting moving images, reproduced images can be prevented from giving any disagreeable impression, for example, by slightly moving the camera to correct an initial defocus state, even in cases where the lens is out of focus in the initial stage or where the focus is on a wrong object due to perspective confusion. Whereas, in the case of still image shooting, the quality of the reproduced image degrades unless shooting is performed in an adequate in-focus state for every frame.
(2) In a system designed intrinsically for the moving image shooting, automatic focusing is performed only to avoid giving a disagreeable impression. Hence, the algorithm of the automatic focusing is not always arranged to be suitable also for the still image shooting.
(3) The moving-image taking camera systems for general consumers are arranged without any function of adjusting the focus by giving priority to the depth of field in general, because this function is not absolutely necessary for such camera systems. In the case of still image shooting, however, it is difficult to obtain images as desired under some conditions without the above-stated function which gives priority to the depth of field.
Further, the conventional camera of the kind mentioned above also has presented the following drawbacks with respect to white balance adjustment control:
(1) If the object happens to change suddenly at the instant of taking a shot of a still image, the white balance adjustment (adjustment of hue) fails to follow the change. In such a case, the shot is apt to be taken to give an image which differs from the actual color of the object in hue, saturation, etc.
(2) In the event of the so-called wash-out which results, for example, from a sudden change in the color temperature of a light source, a short period of time is necessary for reproduction of the actual color. A still image taken before the lapse of this period of time comes to present an unnatural color.
(3) It has been practiced to adjust the white balance by causing the average of color signals of one image plane to become white. Therefore, it has been sometimes impossible to reproduce the color of a part of the image plane. For example, in the case of taking a still image shot of a person standing in front of a large red building, a red color is judged to be white. In this case, the skin color of the person becomes unnatural.
The conventional camera further has had the following drawbacks with respect to exposure control:
In shooting moving images, any wrong aperture position that results from inadequate light measurement during a certain period can be corrected by a generally employed process such as back-light correction or changing the angle of view without giving any disagreeable impression to the viewers of the moving images. Whereas, in the case of still image shooting, once a shot is taken at an inadequate aperture, it is difficult to correct the image not only during the process of shooting but also at the time of reproduction.
Further, the aperture control for the moving image shooting is generally performed to optimize the levels of video signals outputted from an image sensor and also from a signal processing circuit after the image sensor by feeding back information on the output signal level to a diaphragm driving circuit. This arrangement, however, tends to bring about a back-light state or a wash-out state depending on which part of the image plane is used for light measurement.
A particularly important problem lies in that: In recording a still image, only one aperture position is selectable for each moment of shot. If still image shooting is performed depending solely on an automatic aperture adjustment device, therefore, it would sometimes be impossible to make an exposure as desired.
Further, in taking a shot of a still image with an electronic still video camera having a zoom lens, it has been practiced to decide the angle of view by sighting an image within a viewfinder or by seeing moving images on a monitor in the same manner as in the case of moving image shooting. However, the conventional electronic still video camera has shown the following drawbacks:
(1) It is difficult to compare the images of one and the same object obtained at different angles of view because the images of different angles of view cannot be simultaneously seen.
(2) Use of many components such as zoom lens driving system, etc., increases power consumption, which seriously affects the shootable number of frames, because of the limited battery capacity available for the electronic still camera.
(3) In a case where images obtained by moving image shooting are to be monitored, the internal heat generation of the apparatus increases. The internal head then might deteriorate the picture quality of the images recorded. Any attempt to solve this problem by increasing a heat discharging ability would inevitably make the external size of the apparatus larger.